app module build gradle for one of my app

build.gradle

buildscript {
    repositories {
        maven { url 'https://maven.fabric.io/public' }
    }

    dependencies {
        classpath 'io.fabric.tools:gradle:1.21.6'
    }
}
apply plugin: 'com.android.application'
apply plugin: 'io.fabric'

repositories {
    maven { url 'https://maven.fabric.io/public' }
}

apply plugin: 'realm-android'

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.1"
    defaultConfig {
        applicationId "com.xxx"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 28
        versionName "3.2"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        vectorDrawables.useSupportLibrary = true
    }
    applicationVariants.all { variant ->
        variant.resValue "string", "versionName", variant.versionName
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })

    testCompile 'junit:junit:4.12'

    compile('com.crashlytics.sdk.android:crashlytics:2.6.8@aar') {
        transitive = true;
    }

    //google support libraries
    compile 'com.android.support:appcompat-v7:26.0.1'
    compile 'com.android.support:design:26.0.1'
    compile 'com.android.support:cardview-v7:26.0.1'

    //gson
    compile 'com.google.code.gson:gson:2.7'
    compile 'com.squareup.retrofit2:converter-gson:2.2.0'

    //retrofit
    compile 'com.squareup.okhttp3:logging-interceptor:3.6.0'
    compile 'com.squareup.retrofit2:retrofit:2.3.0'
    compile 'com.squareup:otto:1.3.8'

    //volley
    compile 'com.android.volley:volley:1.0.0'

    //glide
    compile 'com.github.bumptech.glide:glide:3.8.0'
    compile 'com.github.bumptech.glide:okhttp3-integration:1.5.0@aar'

    //firebase
    compile 'com.firebase:firebase-jobdispatcher:0.8.2'
    compile 'com.google.firebase:firebase-core:11.4.0'
    compile 'com.google.firebase:firebase-config:11.4.0'

    //butterknife error with proguard
//    compile 'com.jakewharton:butterknife:8.8.1'
//    annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
}

apply plugin: 'com.google.gms.google-services'